Special Senses Lecture Notes PDF

THE SPECIAL SENSES Dr. Gregory Karapetian Lecture 1 1 Introduction to the Special Senses  Five Special Senses  Olfaction  Equilibrium  Gustation  Hearing  Vision 2...

THE SPECIAL SENSES Dr. Gregory Karapetian Lecture 1 1 Introduction to the Special Senses  Five Special Senses  Olfaction  Equilibrium  Gustation  Hearing  Vision 2 1  Olfaction: Smell  Olfactory Organs  Provide sense of smell  Located in nasal cavity on either side of nasal septum  Made up of two layers: ◼ Olfactory epithelium ◼ Lamina propria Olfactory Organs – located within 3 Olfaction: Smell  Layers of olfactory organs  Olfactory epithelium: ◼ Olfactory receptors ◼ Supporting cells ◼ Basal (stem) cells  Lamina propria: ◼ Areolar tissue ◼ Blood vessels ◼ Nerves ◼ Olfactory glands 4 2  The Olfactory Organs 5 Olfaction: Smell  Olfactory Glands  Secretions coat surfaces of olfactory organs  Olfactory Receptors  Specialized neurons involved in olfactory reception – detecting dissolved chemicals interacting with odorant-binding proteins 6 3  Olfaction: Smell  Olfactory pathways follow the axons leaving the olfactory epithelium  Collect into 20+ bundles  Penetrate cribriform plate of ethmoid  Reach olfactory bulbs of cerebrum – where the first synapse occurs Cribriform Plate  Axons leaving olfactory bulb travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system 7 Olfaction: Smell  Olfactory Pathways  Arriving information reaches information centers without always first synapsing in thalamus 8 4  Olfaction: Smell  Olfactory Discrimination  We can distinguish thousands of chemical stimuli  CNS interprets smells by the pattern of receptor activity  There is a considerable turnover of the olfactory receptor population  Number of olfactory receptors declines with age 9 Gustation: Taste  Gustation provides information about the foods and liquids we consume  Taste receptors (gustatory receptors) are distributed on tongue and portions of pharynx and larynx  Clustered into taste buds 10 5  Gustation: Taste  Taste buds contain  Basal (stem) cells  Gustatory cells ◼ Extend taste hairs through taste pore ◼ Survive about 10 days Taste buds before replacement 11 Gustatory Receptors  Taste buds are integrated with lingual papillae (projections) on the surface of the tongue  Filiform papillae  Fungiform papillae  Circumvallate papillae 12 6  Gustatory Discrimination  Dissolved chemicals contact taste hairs  Bind to receptor proteins of gustatory cell  Activate chemically gated ion channels  Stimulation produces depolarization of cell  Release of neurotransmitters  Neurotransmitters generate action potentials AP 13 Gustation: Taste  Gustatory Discrimination  Taste Sensitivity  Exhibits significant individual differences  Some conditions are inherited ◼ Ex: phenylthiocarbamide (PTC): ◼ 70% of people taste it, but 30% do not  Number of taste buds ◼ Begins declining rapidly by age 50 14 7  Vision: The Eye  Accessory Structures of the Eye  Provide protection, lubrication, and support  Include: 1. Palpebrae (eyelids) 2. Superficial epithelium of eye 3. Lacrimal apparatus The superficial eye 15 Structures of the Eye (1 of 3)  Palpebrae (Eyelids)  Continuation of skin  Blinking keeps surface of eye lubricated, free of dust and debris  Palpebral fissure ◼ Gap that separates free margins of upper and lower eyelids 16 8  Structures of the Eye (2 of 3)  Superficial Epithelium of Eye  Lacrimal caruncle is a mass of soft tissue that contains glands producing thick secretions ◼ Generates “sand-like” deposits after sleeping at night 17 Structures of the Eye (2 of 3)  Superficial Epithelium of Eye  Conjunctiva ◼ Epithelium covering outer surface of eye – ocular conjunctiva ◼ Epithelium covering inner surfaces of eyelids – palpebral conjunctiva Viral conjunctivitis 18 9  Structures of the Eye (3 of 3)  Lacrimal Apparatus  Produces, distributes, and drains tears  Lacrimal gland is the “tear gland” ◼ Secretions contain lysozyme – an antibacterial enzyme 19 Sectional Anatomy of the Eye 20 10  The Eye  Three Layers of the Eye 1. Outer fibrous tunic Fibrous 2. Middle vascular tunic Neural 3. Inner neural tunic  Eyeball  Hollow Vascular  Divided into two cavities: ◼ Large posterior segment ◼ Smaller anterior segment 21 The Eye: Fibrous Tunic (1 of 3)  Sclera – white of the eye  Cornea – initial structure to “bend” entering light  The limbus is the border between the cornea and sclera Sclera Cornea 22 11  The Eye: Vascular Tunic (2 of 3)  The Choroid (also: the Uvea)  Vascular layer between fibrous and neural tunics  Blood vessels here deliver oxygen and nutrients to retina  Secretes and reabsorbs aqueous humor that circulates within chambers of eye 23 The Eye: Vascular Tunic (2 of 3)  The location of the iris and ciliary muscle  The iris contains both pupillary dilator and constrictor muscles ◼ Change the diameter of pupil, thereby regulating amount of light entering eye  Ciliary Muscle ◼ Controls shape of lens, which is essential to focusing 24 12  The Pupillary Dilator and Constrictor Muscles 25 The Eye: Neural Tunic (3 of 3)  The Retina  Outer layer called: Pigmented part  Inner Neural part ◼ Contains visual receptors and associated neurons ◼ Rods and cones are types of photoreceptors: ◼ Rods ◼ Do not discriminate light colors ◼ Highly sensitive to light ◼ Cones ◼ Provide color vision ◼ Densely clustered in fovea, at center of macula lutea 26 13  The Retina in Diagrammatic Sagittal Section 27 The Eye: Neural Tunic (3 of 3)  Fovea is the region just lateral to the optic disc  Optic Disc is the origin of optic nerve – blind spot Photograph of the retina as seen through the pupil 28 14  Glaucoma  Over time the optic nerve becomes damaged, usually due to high intraocular pressure Poor flow of aqueous humor 29 Age-Related Macular Degeneration  Deterioration of the macula (location of fovea) Macula Optic disc Fovea “Dry” ARMD accounts for ~90% “Wet” Macular “Dry” Macular Degeneration Degeneration Results in loss of central vision 30 15  Demonstration of the Presence of a Blind Spot 31 The Eye  Ciliary body and lens divide eye  Small anterior segment ◼ Anterior chamber: ◼ Extends from cornea to iris ◼ Posterior chamber: ◼ Extends from iris to lens  Large posterior segment ◼ Extends from lens to the posterior of the eye ◼ Vitreous humor – gelatinous mass stabilizes shape, supports retina 32 16  The Eye  Smaller anterior segment  Aqueous humor ◼ Fluid circulates within anterior eye ◼ Diffuses through walls of anterior chamber into Canal of Schlemm ◼ Re-enters circulation  Intraocular pressure ◼ Fluid pressure in aqueous humor ◼ Helps retain eye shape 33 The Circulation of Aqueous Humor 34 17  The Eye  The lens is the main structure involved in:  Light refraction ◼ Bending of light by cornea and lens Intraocular Lens (IOL) used in cataract surgery  Focal point ◼ Specific point of intersection on retina  Focal distance ◼ Distance between center of lens and focal point 35 Factors Affecting Focal Distance  Accommodation  Shape of lens changes to focus image on retina 36 18  Accommodation 37 Visual Abnormalities 38 19  Visual Abnormalities 39 The Eye  Astigmatism  Curvature of cornea is oblong, so light passing through is not refracted properly  Visual image is distorted  Visual acuity  Clarity of vision  “Normal” rating is 20/20 40 20  Image Formation 41 Visual Physiology: Photoreceptors  Rods  Respond to almost any photon (they do not discriminate light colors), regardless of energy content  Cones  Color vision is the integration of information from red, green, and blue cones  Color blindness – the inability to detect certain colors 42 21  Standard Test for Color Vision 43 Visual Physiology  Central Processing of Visual Information  Axons from ganglion cells converge on optic disc ◼ Ganglion cells: M cells monitor rods, P cells monitor cones  Axons penetrate wall of eye and proceed as the two optic nerves (one for each eye) to reach diencephalon Cranial Nerve II the Optic Nerve at the optic chiasm 44 22  Visual Physiology  Visual data from a combined field of vision arrives at the visual cortex of the occipital lobes  Lateral (retinal) information stays within its respective hemisphere, while medial (retinal) info crosses to opposite hemisphere  Optic radiation  Bundle of projection fibers linking lateral geniculate with visual cortex Cranial Nerve II the Optic Nerve 45 Visual Physiology  The Field of Vision  Experiencing depth perception occurs by comparing relative positions of objects between left-eye and right-eye images  The Brain Stem and Visual Processing  Circadian rhythms ◼ Related to the day-night cycle ◼ Affects other metabolic processes within the body 46 23   The visual pathway must also consider the field of vision 47 24